Polymeric resins have been used in treads of tires to improve traction. Unfortunately, one consequence of their use is a decrease in durability and treadwear.
Polymeric resinous materials containing units derived from piperylene, units derived from 2-methyl-2-butene and units derived from dicyclopentadiene are commercially available from The Goodyear Tire and Rubber Company under the designation WINGTACK(copyright) 115. These polymeric resinous materials find use in adhesives.
The present invention relates to a polymeric resinous material derived from limonene, dicyclopentadiene, indene and tert-butyl styrene.
There is disclosed a polymeric resinous material comprising
(a) from 5 to 70 weight percent units derived from limonene;
(b) from 5 to 70 weight percent units derived from dicyclopentadiene;
(c) from 5 to 45 weight percent units derived from indene; and
(d) from 5 to 45 weight percent units derived from tertiary-butyl styrene;
wherein the sum of the weight percent units derived from limonene and dicyclopentadiene range from 40 to 75 weight percent units of the resin and the sum of the weight percent units derived from indene and tertiary-butyl styrene range from 25 to 60 weight percent units of the resin.
In addition, there is disclosed a rubber composition comprising (a) a diene-based elastomer containing olefinic unsaturation and (b) 1 to 80 phr of a polymeric resinous material comprising
(1) from 5 to 70 weight percent units derived from limonene;
(2) from 5 to 70 weight percent units derived from dicyclopentadiene;
(3) from 5 to 45 weight percent units derived from indene; and
(4) from 5 to 45 weight percent units derived from tertiary-butyl styrene;
wherein the sum of the weight percent units derived from limonene and dicyclopentadiene range from 40 to 75 weight percent units of the resin and the sum of the weight percent units derived from indene and tertiary-butyl styrene range from 25 to 60 weight percent units of the resin.
In addition, there is disclosed a pneumatic tire having a tread comprised of (a) a diene-based elastomer containing olefinic unsaturation and (b) 1 to 80 phr of a polymeric resinous material comprising
(1) from 5 to 70 weight percent units derived from limonene;
(2) from 5 to 70 weight percent units derived from dicyclopentadiene;
(3) from 5 to 45 weight percent units derived from indene; and
(4) from 5 to 45 weight percent units derived from tertiary-butyl styrene;
wherein the sum of the weight percent units derived from limonene and dicyclopentadiene range from 40 to 75 weight percent units of the resin and the sum of the weight percent units derived from indene and tertiary-butyl styrene range from 25 to 60 weight percent units of the resin.
The polymeric resinous material for use in the present invention comprises from about 5 to about 70 weight percent units derived from limonene; from about 5 to about 70 weight percent units derived from dicyclopentadiene; from 5 to 45 weight percent units derived from indene; and 5 to 45 weight percent units derived from tertiary-butyl styrene. Preferably, the resin comprises from about 20 to about 30 weight percent units derived from limonene; from about 20 to about 30 weight percent units derived from dicyclopentadiene; from about 20 to about 30 weight percent units derived from indene; and from 20 to 30 weight percent units derived from tertiary-butyl styrene.
In a particularly preferred embodiment, the weight ratio of units derived from limonene:dicyclopentadiene:indene:tertiary-butyl styrene is 1:1:1:1.
The polymeric resin is particularly suited for use in a diene-based elastomer in an amount ranging from about 1 to 80 phr (parts by weight per 100 parts by weight of rubber). Preferably, the polymeric resin is present in an amount ranging from 20 to 40 phr.
The resins may be prepared using various anhydrous metallic halide catalysts. Representative examples of such-catalysts are fluorides, chlorides and bromides, of aluminum, tin and boron. Such catalysts include, for example, aluminum chloride, stannic chloride and boron trifluoride. Alkyl aluminum dihalides are also suitable, representative examples of which are methyl aluminum dichloride, ethyl aluminum dichloride and isopropyl aluminum dichloride.
In carrying out the polymerization reaction, the hydrocarbon mixture is brought into contact with the anhydrous halide catalyst. Generally, the catalyst is used in particulate form having a particle size in the range of from about 5 to about 200 mesh size, although larger or smaller particles can be used. The amount of catalyst used is not critical although sufficient catalyst must be used to cause a polymerization reaction to occur. The catalyst may be added to the olefinic hydrocarbon mixture or the hydrocarbon mixture may be added to the catalyst. If desired, the catalyst and mixture of hydrocarbons can be added simultaneously or intermittently to a reactor. The reaction can be conducted continuously or by batch process techniques generally known to those skilled in the art.
The reaction is conveniently carried out in the presence of a diluent because it is usually exothermic. Various diluents which are inert in that they do not enter into the polymerization reaction may be used. Representative examples of inert diluents are aliphatic hydrocarbons such as pentane, hexane, cyclohexane and heptane, aromatic hydrocarbons such as toluene, xylene and benzene, and unreacted residual hydrocarbons from the reaction.
A wide range of temperatures can be used for the polymerization reaction. The polymerization can be carried out at temperatures in the range of from about xe2x88x9220xc2x0 C. to about 100xc2x0 C., although usually the reaction is carried out at a temperature in the range of from about 0xc2x0 C. to about 50xc2x0 C. The polymerization reaction pressure is not critical and may be atmospheric or above or below atmospheric pressure. Generally, a satisfactory polymerization can be conducted when the reaction is carried out at about autogenous pressure developed by the reactor under the operating conditions used. The time of the reaction is not generally critical and reaction times can vary from a few seconds to 12 hours or more.
Upon completion of the reaction the hydrocarbon mixture is neutralized followed by isolation of the resin solution. The resin solution is steam-distilled with the resulting matter resin being allowed to cool.
The resins can optionally be modified by the addition of up to about 25 weight percent of other unsaturated hydrocarbons and particularly hydrocarbons containing from 9 to 10 carbon atoms and mixtures thereof. Representative examples of such hydrocarbons are 3-methyl styrene, 4-methyl styrene, 1-methyl indene, 2-methyl indene, 3-methyl indene and mixtures thereof.
The resinous materials of this invention are characterized by having a Gardner color of from about 2 to about 10, a softening point of from about 100xc2x0 C. to about 160xc2x0 C., according to ASTM Method E28, good heat stability and a specific gravity of from about 0.85 to about 1.0. They typically have a softening point of 100xc2x0 C. to 160xc2x0 C. after steam-stripping to remove lower molecular weight compounds; although, when prepared in the presence of a chlorinated hydrocarbon solvent, their softening point is increased within that range. These resins are generally soluble in aliphatic hydrocarbons such as pentane, hexane, heptane and aromatic hydrocarbons such as benzene and toluene.
The tread of the tire of the present invention contains an elastomer containing olefinic unsaturation. The phrase xe2x80x9crubber or elastomer containing olefinic unsaturationxe2x80x9d is intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers. In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber composition,xe2x80x9d xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art. Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. Specific examples of synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene), butyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM) and, in particular, ethylene/propylene/dicyclopentadiene terpolymers. The preferred rubber or elastomers are polybutadiene and SBR.
In one aspect, the rubber is preferably of at least two of diene-based rubbers. For example, a combination of two or more rubbers is preferred such as cis 1,4-polyisoprene rubber (natural or synthetic, although natural is preferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers.
In one aspect of this invention, an emulsion polymerization derived styrene/butadiene (E-SBR) might be used having a relatively conventional styrene content of about 20 to about 28 weight percent bound styrene or, for some applications, an E-SBR having a medium to relatively high bound styrene content; namely, a bound styrene content of about 30 to about 45 percent.
The relatively high styrene content of about 30 to about 45 for the E-SBR can be considered beneficial for a purpose of enhancing traction, or skid resistance, of the tire tread. The presence of the E-SBR itself is considered beneficial for a purpose of enhancing processability of the uncured elastomer composition mixture, especially in comparison to a utilization of a solution polymerization prepared SBR (S-SBR).
By emulsion polymerization prepared E-SBR, it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art. The bound styrene content can vary, for example, from about 5 to about 50 percent. In one aspect, the E-SBR may also contain acrylonitrile to form a terpolymer rubber, as E-SBAR, in amounts, for example, of about 2 to about 30 weight percent bound acrylonitrile in the terpolymer.
Emulsion polymerization prepared styrene/butadiene/acrylonitrile terpolymer rubbers containing about 2 to about 40 weight percent bound acrylonitrile in the terpolymer are also contemplated as diene-based rubbers for use in this invention.
The solution polymerization prepared SBR (S-SBR) typically has a bound styrene content in a range of about 5 to about 50, preferably about 9 to about 36, percent. The S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.
A purpose of using S-SBR is for improved tire rolling resistance as a result of lower hysteresis when it is used in a tire tread composition.
The 3,4-polyisoprene rubber (3,4-PI) is considered beneficial for a purpose of enhancing the tire""s traction when it is used in a tire tread composition. The 3,4-PI and use thereof is more fully described in U.S. Pat. No. 5,087,668 which is incorporated herein by reference. The Tg refers to the glass transition temperature which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10xc2x0 C. per minute.
The cis 1,4-polybutadiene rubber (BR) is considered to be beneficial for a purpose of enhancing the tire tread""s wear, or treadwear. Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.
The cis 1,4-polyisoprene (synthetic) and cis 1,4-polyisoprene natural rubber are well known to those having skill in the rubber art.
The term xe2x80x9cphrxe2x80x9d as used herein, and according to conventional practice, refers to xe2x80x9cparts by weight of a respective material per 100 parts by weight of rubber, or elastomer.xe2x80x9d
In one embodiment, the rubber composition in the tread contains a sufficient amount of filler to contribute a reasonably high modulus and high resistance to tear. The filler may be added in amounts ranging from 10 to 250 phr. When the filler is silica, the silica is generally present in an amount ranging from 10 to 80 phr. Preferably, the silica is present in an amount ranging from 15 to 70 phr. When the filler is carbon black, the amount of carbon black will vary from 0 to 80 phr. Preferably, the amount of carbon black will range from 0 to 40 phr.
The commonly employed particulate precipitated silica used in rubber compounding applications can be used as the silica in this invention. These precipitated silicas include, for example, those obtained by the acidification of a soluble silicate; e.g., sodium silicate.
Such silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, page 304 (1930).
The silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, and more usually about 150 to about 300.
The silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.
Various commercially available silicas may be considered for use in this invention such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc; silicas available from Rhone-Poulenc, with, for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3, etc.
The processing of the sulfur vulcanizable rubber may be conducted in the presence of a sulfur containing organosilicon compound. Examples of suitable sulfur containing organosilicon compounds are of the formula:
Zxe2x80x94Alkxe2x80x94Snxe2x80x94Alkxe2x80x94Zxe2x80x83xe2x80x83(I)
in which Z is selected from the group consisting of 
where
R1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;
R2 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms;
Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8.
Specific examples of sulfur containing organosilicon compounds which may be used in accordance with the present invention include: 3,3xe2x80x2-bis(trimethoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)octasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(triethoxysilylethyl)tetrasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(tributoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)hexasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)octasulfide, 3,3xe2x80x2-bis(trioctoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(trihexoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(tri-2xe2x80x3-ethylhexoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triisooctoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(tri-t-butoxysilylpropyl)disulfide, 2,2xe2x80x2-bis(methoxy diethoxy silyl ethyl)tetrasulfide, 2,2xe2x80x2-bis(tripropoxysilylethyl)pentasulfide, 3,3xe2x80x2-bis(tricyclohexoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(tricyclopentoxysilylpropyl)trisulfide, 2,2xe2x80x2-bis(tri-2xe2x80x3-methylcyclohexoxysilylethyl)tetrasulfide, bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl 3xe2x80x2-diethoxybutoxy-silylpropyltetrasulfide, 2,2xe2x80x2-bis(dimethyl methoxysilylethyl)disulfide, 2,2xe2x80x2-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3xe2x80x2-bis(methyl butylethoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(di t-butylmethoxysilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(phenyl methylmethoxysilylethyl)trisulfide, 3,3xe2x80x2-bis(diphenyl isopropoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(diphenyl cyclohexoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(dimethyl ethylmercaptosilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(methyl dimethoxysilylethyl)trisulfide, 2,2xe2x80x2-bis(methyl ethoxypropoxysilylethyl)tetrasulfide, 3,3xe2x80x2-bis(diethyl methoxysilylpropyl)tetrasulfide, 3,31-bis(ethyl di-sec. butoxysilylkpropyl)disulfide, 3,3xe2x80x2-bis(propyl diethoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(butyl dimethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(phenyl dimethoxysilylpropyl)tetrasulfide, 3-phenyl ethoxybutoxysilyl 3xe2x80x2-trimethoxysilylpropyl tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilylbutyl)tetrasulfide, 6,6xe2x80x2-bis(triethoxysilylhexyl)tetrasulfide, 12,12xe2x80x2-bis(triisopropoxysilyl dodecyl)disulfide, 18,18xe2x80x2-bis(trimethoxysilyloctadecyl)tetrasulfide, 18,18xe2x80x2-bis(tripropoxysilyloctadecenyl)tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilyl-buten-2-yl)tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilylcyclohexylene)tetrasulfide, 5,5xe2x80x2-bis(dimethoxymethylsilylpentyl)trisulfide, 3,3xe2x80x2-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide, 3,3xe2x80x2-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.
The preferred sulfur containing organosilicon compounds are the 3,3xe2x80x2-bis(trimethoxy or triethoxy silylpropyl)sulfides. The most preferred compound is 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to Formula I, preferably Z is 
where R2 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularly preferred; Alk is a divalent hydrocarbon of 2 to 4 carbon atoms, with 3 carbon atoms being particularly preferred; and n is an integer of from 3 to 5, with 4 being particularly preferred.
The amount of the sulfur containing organosilicon compound of Formula I in a rubber composition will vary depending on the level of silica that is used. Generally speaking, the amount of the compound of formula II, if used, will range from 0.01 to 1.0 parts by weight per part by weight of the silica. Preferably, the amount will range from 0.05 to 0.4 parts by weight per part by weight of the silica.
The rubber compositions of the present invention may contain a methylene donor and a methylene acceptor. The term xe2x80x9cmethylene donorxe2x80x9d is intended to mean a compound capable of reacting with a methylene acceptor (such as resorcinol or its equivalent containing a present hydroxyl group) and generate the resin in-situ. Examples of methylene donors which are suitable for use in the present invention include hexamethylenetetramine, hexaethoxymethylmelamine, hexamethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, the hydroxy groups of which may be esterified or partly esterified, and polymers of formaldehyde such as paraformaldehyde. In addition, the methylene donors may be N-substituted oxymethylmelamines, of the general formula: 
wherein X is an alkyl having from 1 to 8 carbon atoms, R3, R4, R5, R6 and R7 are individually selected from the group consisting of hydrogen, an alkyl having from 1 to 8 carbon atoms and the group xe2x80x94CH2OX. Specific methylene donors include hexakis-(methoxymethyl)melamine, N,Nxe2x80x2,Nxe2x80x3-trimethyl/N,Nxe2x80x2,Nxe2x80x3-trimethylolmelamine, hexamethylolmelamine, N,Nxe2x80x2,Nxe2x80x3-dimethylolmelamine, N-methylolmelamine, N,Nxe2x80x2-dimethylolmelamine, N,Nxe2x80x2,Nxe2x80x3-tris(methoxymethyl)melamine and N,Nxe2x80x2Nxe2x80x3-tributyl-N,Nxe2x80x2,Nxe2x80x3-trimethylol-melamine. The N-methylol derivatives of melamine are prepared by known methods.
The amount of methylene donor and methylene acceptor that is present in the rubber stock may vary. Typically, the amount of methylene donor and methylene acceptor that are present will range from about 0.1 phr to 10.0 phr. Preferably, the amount of methylene donor and methylene acceptor ranges from about 2.0 phr to 5.0 phr for each.
The weight ratio of methylene donor to the methylene acceptor may vary. Generally speaking, the weight ratio will range from about 1:10 to about 10:1. Preferably, the weight ratio ranges from about 1:3 to 3:1.
It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned below are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. Preferably, the sulfur vulcanizing agent is elemental sulfur. The sulfur vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, with a range of from 1.5 to 6 phr being preferred. Typical amounts of processing oils comprise about 1 to about 50 phr. Such processing aids can include, for example, aromatic, naphthenic and/or paraffinic processing oils. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in the Vanderbilt Rubber Handbook (1978), pages 344-346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids, if used, which can include stearic acid comprise about 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typical amounts of microcrystalline and paraffinic waxes comprise about 1 to about 10 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.
Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system may be used; i.e., primary accelerator. The primary accelerator(s) may be used in total amounts ranging from about 0.5 to about 4, preferably about 0.8 to about 1.5, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from about 0.05 to about 3 phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.
The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients are typically mixed in at least two stages; namely, at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur vulcanizing agents are typically mixed in the final stage which is conventionally called the xe2x80x9cproductivexe2x80x9d mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The rubber and polymeric resin are mixed in one or more non-productive mix stages. The terms xe2x80x9cnon-productivexe2x80x9d and xe2x80x9cproductivexe2x80x9d mix stages are well known to those having skill in the rubber mixing art.
Vulcanization of the pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100xc2x0 C. to 200xc2x0 C. Preferably, the vulcanization is conducted at temperatures ranging from about 110xc2x0 C. to 180xc2x0 C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air or in a salt bath.
The following examples are presented in order to illustrate but not limit the present invention.
Cure properties were determined using a Monsanto oscillating disc rheometer which was operated at a temperature of 150xc2x0 C. and at a frequency of 11 hertz. A description of oscillating disc rheometers can be found in the Vanderbilt Rubber Handbook edited by Robert O. Ohm (Norwalk, Conn., R. T. Vanderbilt Company, Inc., 1990), pages 554-557. The use of this cure meter and standardized values read from the curve are specified in ASTM D-2084. A typical cure curve obtained on an oscillating disc rheometer is shown on page 555 of the 1990 edition of the Vanderbilt Rubber Handbook.
In such an oscillating disc rheometer, compounded rubber samples are subjected to an oscillating shearing action of constant amplitude. The torque of the oscillating disc embedded in the stock that is being tested that is required to oscillate the rotor at the vulcanization temperature is measured. The values obtained using this cure test are very significant since changes in the rubber or the compounding recipe are very readily detected. It is obvious that it is normally advantageous to have a fast cure rate.
In the following examples, the Flexsys Rubber Process Analyzer (RPA) 2000 was used to determine dynamic mechanical rheological properties. The curing conditions were 160xc2x0 C., 1.667 Hz, 15.8 minutes and 0.7 percent strain. A description of the RPA 2000, its capability, sample preparation, tests and subtests can be found in these references. H A Pawlowski and J S Dick, Rubber World, June 1992; J S Dick and H A Pawlowski, Rubber World, January 1997; and J S Dick and J A Pawlowski, Rubber and Plastics News, April 26 and May 10, 1993.
The compounded rubber sample is placed on the bottom die. When the dies are brought together, the sample is in a pressurized cavity where it will be subjected to a sinusoidal oscillating shearing action of the bottom die. A torque transducer connected to the upper die measures the amount of torque transmitted through the sample as a result of the oscillations. Torque is translated into the shear modulus, G, by correcting for the die form factor and the strain. The RPA 2000 is capable of testing uncured or cured rubber with a high degree of repeatability and reproducibility. The tests and subtests available include frequency sweeps at constant temperature and strain, curing at constant temperature and frequency, strain sweeps at constant temperature and frequency and temperature sweeps at constant strain and frequency. The accuracy and precision of the instrument allows reproducible detection of changes in the compounded sample.
The values reported for the storage modulus, (Gxe2x80x2), loss compliance (Jxe2x80x3) and tan delta are obtained from a strain sweep at 100xc2x0 C. and 1 Hz following the cure test. These properties represent the viscoelastic response of a test sample to shear deformation at a constant temperature and frequency.